jeudi 25 mai 2017

US nuclear regulators greatly underestimate potential for nuclear disaster

The U.S. Nuclear Regulatory Commission (NRC) relied on faulty analysis to justify its refusal to adopt a critical measure for protecting Americans from the occurrence of a catastrophic nuclear-waste fire at any one of dozens of reactor sites around the country, according to an article in the May 26 issue of Science magazine. Fallout from such a fire could be considerably larger than the radioactive emissions from the 2011 Fukushima accident in Japan.

Published by researchers from Princeton University and the Union of Concerned Scientists, the article argues that NRC inaction leaves the public at high risk from fires in spent-nuclear-fuel cooling pools at reactor sites. The pools -- water-filled basins that store and cool used radioactive fuel rods -- are so densely packed with nuclear waste that a fire could release enough radioactive material to contaminate an area twice the size of New Jersey. On average, radioactivity from such an accident could force approximately 8 million people to relocate and result in $2 trillion in damages.

These catastrophic consequences, which could be triggered by a large earthquake or a terrorist attack, could be largely avoided by regulatory measures that the NRC refuses to implement. Using a biased regulatory analysis, the agency excluded the possibility of an act of terrorism as well as the potential for damage from a fire beyond 50 miles of a plant. Failing to account for these and other factors led the NRC to significantly underestimate the destruction such a disaster could cause.

"The NRC has been pressured by the nuclear industry, directly and through Congress, to low-ball the potential consequences of a fire because of concerns that increased costs could result in shutting down more nuclear power plants," said paper co-author Frank von Hippel, a senior research physicist at Princeton's Program on Science and Global Security (SGS), based at the Woodrow Wilson School of Public and International Affairs. "Unfortunately, if there is no public outcry about this dangerous situation, the NRC will continue to bend to the industry's wishes."

Von Hippel's co-authors are Michael Schoeppner, a former postdoctoral researcher at Princeton's SGS, and Edwin Lyman, a senior scientist at the Union of Concerned Scientists.

Spent-fuel pools were brought into the spotlight following the March 2011 nuclear disaster in Fukushima, Japan. A 9.0-magnitude earthquake caused a tsunami that struck the Fukushima Daiichi nuclear power plant, disabling the electrical systems necessary for cooling the reactor cores. This led to core meltdowns at three of the six reactors at the facility, hydrogen explosions, and a release of radioactive material.

"The Fukushima accident could have been a hundred times worse had there been a loss of the water covering the spent fuel in pools associated with each reactor," von Hippel said. "That almost happened at Fukushima in Unit 4."

In the aftermath of the Fukushima disaster, the NRC considered proposals for new safety requirements at U.S. plants. One was a measure prohibiting plant owners from densely packing spent-fuel pools, requiring them to expedite transfer of all spent fuel that has cooled in pools for at least five years to dry storage casks, which are inherently safer. Densely packed pools are highly vulnerable to catching fire and releasing huge amounts of radioactive material into the atmosphere.

The NRC analysis found that a fire in a spent-fuel pool at an average nuclear reactor site would cause $125 billion in damages, while expedited transfer of spent fuel to dry casks could reduce radioactive releases from pool fires by 99 percent. However, the agency decided the possibility of such a fire is so unlikely that it could not justify requiring plant owners to pay the estimated cost of $50 million per pool.

The NRC cost-benefit analysis assumed there would be no consequences from radioactive contamination beyond 50 miles from a fire. It also assumed that all contaminated areas could be effectively cleaned up within a year. Both of these assumptions are inconsistent with experience after the Chernobyl and Fukushima accidents.

In two previous articles, von Hippel and Schoeppner released figures that correct for these and other errors and omissions. They found that millions of residents in surrounding communities would have to relocate for years, resulting in total damages of $2 trillion -- nearly 20 times the NRC's result. Considering the nuclear industry is only legally liable for $13.6 billion, thanks to the Price Anderson Act of 1957, U.S. taxpayers would have to cover the remaining costs.

The authors point out that if the NRC does not take action to reduce this danger, Congress has the authority to fix the problem. Moreover, the authors suggest that states that provide subsidies to uneconomical nuclear reactors within their borders could also play a constructive role by making those subsidies available only for plants that agreed to carry out expedited transfer of spent fuel.

"In far too many instances, the NRC has used flawed analysis to justify inaction, leaving millions of Americans at risk of a radiological release that could contaminate their homes and destroy their livelihoods," said Lyman. "It is time for the NRC to employ sound science and common-sense policy judgments in its decision-making process."

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US nuclear regulators greatly underestimate potential for nuclear disaster

Why the Sumatra earthquake was so severe

An international team of scientists has found evidence suggesting the dehydration of minerals deep below the ocean floor influenced the severity of the Sumatra earthquake, which took place on December 26, 2004.

The earthquake, measuring magnitude 9.2, and the subsequent tsunami, devastated coastal communities of the Indian Ocean, killing over 250,000 people.

Research into the earthquake was conducted during a scientific ocean drilling expedition to the region in 2016, as part of the International Ocean Discovery Program (IODP), led by scientists from the University of Southampton and Colorado School of Mines.

During the expedition on board the research vessel JOIDES Resolution, the researchers sampled, for the first time, sediments and rocks from the oceanic tectonic plate which feeds the Sumatra subduction zone. A subduction zone is an area where two of the Earth's tectonic plates converge, one sliding beneath the other, generating the largest earthquakes on Earth, many with destructive tsunamis.

Findings of a study on sediment samples found far below the seabed are now detailed in a new paper led by Dr Andre Hüpers of the MARUM-Center for Marine Environmental Sciences at University of Bremen - published in the journal Science.

Expedition co-leader Professor Lisa McNeill, of the University of Southampton, says: "The 2004 Indian Ocean tsunami was triggered by an unusually strong earthquake with an extensive rupture area. We wanted to find out what caused such a large earthquake and tsunami and what this might mean for other regions with similar geological properties."

The scientists concentrated their research on a process of dehydration of sedimentary minerals deep below the ground, which usually occurs within the subduction zone. It is believed this dehydration process, which is influenced by the temperature and composition of the sediments, normally controls the location and extent of slip between the plates, and therefore the severity of an earthquake.

In Sumatra, the team used the latest advances in ocean drilling to extract samples from 1.5 km below the seabed. They then took measurements of sediment composition and chemical, thermal, and physical properties and ran simulations to calculate how the sediments and rock would behave once they had travelled 250 km to the east towards the subduction zone, and been buried significantly deeper, reaching higher temperatures.

The researchers found that the sediments on the ocean floor, eroded from the Himalayan mountain range and Tibetan Plateau and transported thousands of kilometres by rivers on land and in the ocean, are thick enough to reach high temperatures and to drive the dehydration process to completion before the sediments reach the subduction zone. This creates unusually strong material, allowing earthquake slip at the subduction fault surface to shallower depths and over a larger fault area - causing the exceptionally strong earthquake seen in 2004.

Dr Andre Hüpers of the University of Bremen says: "Our findings explain the extent of the large rupture area, which was a feature of the 2004 earthquake, and suggest that other subduction zones with thick and hotter sediment and rocks, could also experience this phenomenon.

"This will be particularly important for subduction zones with limited or no historic subduction earthquakes, where the hazard potential is not well known. Subduction zone earthquakes typically have a return time of a few hundred to a thousand years. Therefore our knowledge of previous earthquakes in some subduction zones can be very limited."

Similar subduction zones exist in the Caribbean (Lesser Antilles), off Iran and Pakistan (Makran), and off western USA and Canada (Cascadia). The team will continue research on the samples and data obtained from the Sumatra drilling expedition over the next few years, including laboratory experiments and further numerical simulations, and they will use their results to assess the potential future hazards both in Sumatra and at these comparable subduction zones.

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Magnetic switch turns strange quantum property on and off

When a ballerina pirouettes, twirling a full revolution, she looks just as she did when she started. But for electrons and other subatomic particles, which follow the rules of quantum theory, that's not necessarily so. When an electron moves around a closed path, ending up where it began, its physical state may or may not be the same as when it left.

Now, there is a way to control the outcome, thanks to an international research group led by scientists at the National Institute of Standards and Technology (NIST). The team has developed the first switch that turns on and off this mysterious quantum behavior. The discovery promises to provide new insight into the fundamentals of quantum theory and may lead to new quantum electronic devices.

To study this quantum property, NIST physicist and fellow Joseph A. Stroscio and his colleagues studied electrons corralled in special orbits within a nanometer-sized region of graphene -- an ultrastrong, single layer of tightly packed carbon atoms. The corralled electrons orbit the center of the graphene sample just as electrons orbit the center of an atom. The orbiting electrons ordinarily retain the same exact physical properties after traveling a complete circuit in the graphene. But when an applied magnetic field reaches a critical value, it acts as a switch, altering the shape of the orbits and causing the electrons to possess different physical properties after completing a full circuit.

The researchers report their findings in the May 26, 2017, issue of Science.

The newly developed quantum switch relies on a geometric property called the Berry phase, named after English physicist Sir Michael Berry who developed the theory of this quantum phenomenon in 1983. The Berry phase is associated with the wave function of a particle, which in quantum theory describes a particle's physical state. The wave function -- think of an ocean wave -- has both an amplitude (the height of the wave) and a phase -- the location of a peak or trough relative to the start of the wave cycle.

When an electron makes a complete circuit around a closed loop so that it returns to its initial location, the phase of its wave function may shift instead of returning to its original value. This phase shift, the Berry phase, is a kind of memory of a quantum system's travel and does not depend on time, only on the geometry of the system -- the shape of the path. Moreover, the shift has observable consequences in a wide range of quantum systems.

Although the Berry phase is a purely quantum phenomenon, it has an analog in non-quantum systems. Consider the motion of a Foucault pendulum, which was used to demonstrate Earth's rotation in the 19th century. The suspended pendulum simply swings back and forth in the same vertical plane, but appears to slowly rotate during each swing -- a kind of phase shift -- due to the rotation of Earth beneath it.

Since the mid-1980s, experiments have shown that several types of quantum systems have a Berry phase associated with them. But until the current study, no one had constructed a switch that could turn the Berry phase on and off at will. The switch developed by the team, controlled by a tiny change in an applied magnetic field, gives electrons a sudden and large increase in energy.

Several members of the current research team -- based at the Massachusetts Institute of Technology and Harvard University -- developed the theory for the Berry phase switch.

To study the Berry phase and create the switch, NIST team member Fereshte Ghahari built a high-quality graphene device to study the energy levels and the Berry phase of electrons corralled within the graphene.

First, the team confined the electrons to occupy certain orbits and energy levels. To keep the electrons penned in, team member Daniel Walkup created a quantum version of an electric fence by using ionized impurities in the insulating layer beneath the graphene. This enabled a scanning tunneling microscope at NIST's nanotechnology user facility, the Center for Nanoscale Science and Technology, to probe the quantum energy levels and Berry phase of the confined electrons.

The team then applied a weak magnetic field directed into the graphene sheet. For electrons moving in the clockwise direction, the magnetic field created tighter, more compact orbits. But for electrons moving in counterclockwise orbits, the magnetic field had the opposite effect, pulling the electrons into wider orbits. At a critical magnetic field strength, the field acted as a Berry phase switch. It twisted the counterclockwise orbits of the electrons, causing the charged particles to execute clockwise pirouettes near the boundary of the electric fence.

Ordinarily, these pirouettes would have little consequence. However, says team member Christopher Gutiérrez, "the electrons in graphene possess a special Berry phase, which switches on when these magneticallyinduced pirouettes are triggered."

When the Berry phase is switched on, orbiting electrons abruptly jump to a higher energy level. The quantum switch provides a rich scientific tool box that will help scientists exploit ideas for new quantum devices, which have no analog in conventional semiconductor systems, says Stroscio.

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Magnetic switch turns strange quantum property on and off

Juno mission to Jupiter delivers first science results

NASA's Juno mission, led by Southwest Research Institute's Dr. Scott Bolton, is rewriting what scientists thought they knew about Jupiter specifically, and gas giants in general, according to a pair of Science papers released today. The Juno spacecraft has been in orbit around Jupiter since July 2016, passing within 3,000 miles of the equatorial cloudtops.

"What we've learned so far is earth-shattering. Or should I say, Jupiter-shattering," said Bolton, Juno's principal investigator. "Discoveries about its core, composition, magnetosphere, and poles are as stunning as the photographs the mission is generating."

The solar-powered spacecraft's eight scientific instruments are designed to study Jupiter's interior structure, atmosphere, and magnetosphere. Two instruments developed and led by SwRI are working in concert to study Jupiter's auroras, the greatest light show in the solar system. The Jovian Auroral Distributions Experiment (JADE) is a set of sensors detecting the electrons and ions associated with Jupiter's auroras. The Ultraviolet Imaging Spectrograph (UVS) examines the auroras in UV light to study Jupiter's upper atmosphere and the particles that collide with it. Scientists expected to find similarities to Earth's auroras, but Jovian auroral processes are proving puzzling.

"Although many of the observations have terrestrial analogs, it appears that different processes are at work creating the auroras," said SwRI's Dr. Phil Valek, JADE instrument lead. "With JADE we've observed plasmas upwelling from the upper atmosphere to help populate Jupiter's magnetosphere. However, the energetic particles associated with Jovian auroras are very different from those that power the most intense auroral emissions at Earth."

Also surprising, Jupiter's signature bands disappear near its poles. JunoCam images show a chaotic scene of swirling storms up to the size of Mars towering above a bluish backdrop. Since the first observations of these belts and zones many decades ago, scientists have wondered how far beneath the gas giant's swirling façade these features persist. Juno's microwave sounding instrument reveals that topical weather phenomena extend deep below the cloudtops, to pressures of 100 bars, 100 times Earth's air pressure at sea level.

"However, there's a north-south asymmetry. The depths of the bands are distributed unequally," Bolton said. "We've observed a narrow ammonia-rich plume at the equator. It resembles a deeper, wider version of the air currents that rise from Earth's equator and generate the trade winds."

Juno is mapping Jupiter's gravitational and magnetic fields to better understand the planet's interior structure and measure the mass of the core. Scientists think a dynamo -- a rotating, convecting, electrically conducting fluid in a planet's outer core -- is the mechanism for generating the planetary magnetic fields.

"Juno's gravity field measurements differ significantly from what we expected, which has implications for the distribution of heavy elements in the interior, including the existence and mass of Jupiter's core," Bolton said. The magnitude of the observed magnetic field was 7.766 Gauss, significantly stronger than expected. But the real surprise was the dramatic spatial variation in the field, which was significantly higher than expected in some locations, and markedly lower in others. "We characterized the field to estimate the depth of the dynamo region, suggesting that it may occur in a molecular hydrogen layer above the pressure-induced transition to the metallic state."

These preliminary science results were published in two papers in a special edition of Science. Bolton is lead author of "Jupiter's interior and deep atmosphere: The initial pole-to-pole passes with the Juno spacecraft." SwRI's Dr. Frederic Allegrini, Dr. Randy Gladstone, and Valek are co-authors of "Jupiter's magnetosphere and aurorae observed by the Juno spacecraft during its first polar orbits"; lead author is Dr. John Connerney of the Space Research Corporation.

Juno is the second mission developed under NASA's New Frontiers Program. The first was the SwRI-led New Horizons mission, which provided the first historic look at the Pluto system in July 2015 and is now on its way to a new target in the Kuiper Belt. NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Juno mission for the principal investigator, SwRI's Bolton. Lockheed Martin of Denver built the spacecraft. The Italian Space Agency contributed an infrared spectrometer instrument and a portion of the radio science experiment.

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New species of bus-sized fossil marine reptile unearthed in Russia

A new species of a fossil pliosaur (large predatory marine reptile from the 'age of dinosaur') has been found in Russia and profoundly change how we understand the evolution of the group, says an international team of scientists.

Spanning more than 135 Ma during the 'Age of Dinosaurs', plesiosaur marine reptiles represent one of longest-lived radiations of aquatic tetrapods and certainly the most diverse one. Plesiosaurs possess an unusual body shape not seen in other marine vertebrates with four large flippers, a stiff trunk, and a highly varying neck length. Pliosaurs are a special kind of plesiosaur that are characterized by a large, 2m long skull, enormous teeth and extremely powerful jaws, making them the top predators of oceans during the 'Age of Dinosaurs'.

In a new study to be published today in the journal Current Biology, the team reports a new, exceptionally well-preserved and highly unusual pliosaur from the Cretaceous of Russia (about 130 million years ago). It has been found in Autumn 2002 on right bank of the Volga River, close to the city of Ulyanovsk, by Gleb N. Uspensky (Ulyanovsk State University), one of the co-authors of the paper. The skull of the new species, dubbed "Luskhan itilensis," meaning the Master Spirit from the Volga river, is 1.5m in length, indicating a large animal. But its rostrum is extremely slender, resembling that of fish-eating aquatic animals such as gharials or some species of river dolphins. "This is the most striking feature, as it suggests that pliosaurs colonized a much wider range of ecological niches than previously assumed" said Valentin Fischer, lecturer at the Université de Liège (Belgium) and lead author of the study.

By analysing two new and comprehensive datasets that describe the anatomy and ecomorphology of plesiosaurs with cutting edge techniques, the team revealed that several evolutionary convergences (a biological phenomenon where distantly related species evolve and resemble one another because they occupy similar roles, for example similar feeding strategies and prey types in an ecosystem) took place during the evolution of plesiosaurs, notably after an important extinction event at the end of the Jurassic (145 million years ago). The new findings have also ramifications in the final extinction of pliosaurs, which took place several tens of million years before that of all dinosaurs (except some bird lineages). Indeed, the new results suggest that pliosaurs were able to bounce back after the latest Jurassic extinction, but then faced another extinction that would -- this time -- wipe them off the depths of ancient oceans, forever.

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